The present invention relates to a process for the preparation of substituted pyrazoles and to their use as pesticidal compounds.
Pyrazoles such as 5-amino-1-aryl-3-cyanopyrazole compounds and derivatives thereof, for example fipronil, form an important class of insecticides. Certain substituted 5-N-alkyl-N-alkoxyacetylamino-1-aryl-3-cyanopyrazole compounds also have valuable pesticidal properties, as disclosed in WO00/35884 and U.S. Pat. No. 5,556,873.
U.S. Pat. No. 4,931,461 discloses substituted 5-methylamino-1-aryl pyrazoles and their use as pest-combating agents. These substituted compounds may be prepared in various ways, but in particular it has been found that the compounds may be prepared by reacting the pyrazole with an alkylating agent. This preparation method, while being effective, produces by-products that must be isolated from the desired pesticidal compound.
We have found an alternative route to the production of the aforementioned compounds which reduces and substantially eliminates the presence of by-products, thus avoiding the need to purify the final product.
Accordingly, the present invention provides a process (A) for the preparation of a compound of the formula (I): 
wherein:
R1 is CN or CSNH2;
X is N or CR4;
R2 and R4 are each independently hydrogen or chloro;
R3 is halo, haloalkyl, haloalkoxy or xe2x80x94SF5;
R5 and R6 are each independently alkyl; and
n is 0, 1 or 2;
which process comprises reacting a compound of the formula (II): 
wherein the various symbols are as defined above and W is H, with an alkylating agent of the formula (III):
R6xe2x80x94Yxe2x80x83xe2x80x83(III)
wherein R6 is as defined above and Y is a leaving group.
This process provides the advantage over previously known processes in that this process is more efficient and provides a more direct route to the final product.
It has also been found that, prior to reacting compound (II) with the alkylating agent, compound (II) may be reacted initially with an inorganic metal salt or an organic base, thereby forming an intermediate salt which is then reacted with the alkylating agent.
Thus, according to a second aspect of the present invention there is provided a process (A) for the preparation of a compound of the formula (I) 
wherein:
R1 is CN or CSNH2;
X is N or CR4;
R2 and R4 are each independently hydrogen or chloro;
R3 is halo, haloalkyl, haloalkoxy or xe2x80x94SF5;
R5 and R6 are each independently alkyl; and
n is 0, or 2;
which process comprises (a) a first step of reacting a compound of the formula (II): 
wherein the various symbols are as defined above and W is H, with an inorganic metal salt or an organic base to produce, as an intermediate compound, a salt of said compound of formula (II); and (b) a second step of reacting said salt of said compound of formula (II) with an alkylating agent of the formula (III):
R6xe2x80x94Yxe2x80x83xe2x80x83(III)
wherein R6 is as defined above and Y is a leaving group.